"Gravy is sadly prohibited from carry-on bags unless you pack it in accordance with our liquid policies mentioned above. You can also pack it in your checked baggage." TSA Release on Nov 21, 2017

They don't directly mention any other leftover items. It makes me curious as to the TSA's hatred towards gravy. Was there a gravy mishap that happened to a suit worn by a high-ranking Transportation Security Administration official?

The above mentioned liquid polices is, "...you’re allowed to take as many 3.4 ounce or smaller sized containers that will fit in one sealed, clear, quart-sized zip-top bag – and one bag per person."

That seems like an awful lot of work, so unless the gravy is "to die for", and I doubt it's "I'd go to jail for that gravy" good.

As they expressed, this refers to check-in luggage, so if you hoping to add it to the great airline meal you'll suffer through on the way home, you can do so up to 3.4 ounces. You should be able to add the rests of the gravy into you check-in luggage.